Instrument and system for surgical cutting and evoked potential monitoring

ABSTRACT

A surgical cutting instrument for use with a drive motor, and related system and method, is described. The surgical cutting instrument includes an elongated drive member, a cutting tip secured to the drive member, a non-conductive coupling body adapted for connection to a motor assembly, a housing maintaining the coupling body, and an electrical connector for connection to a stimulating energy source. The electrical connector is in electrical communication with the cutting tip via an electrical pathway.

BACKGROUND

The present invention relates to surgical cutting and surgical cuttinginstruments. More particularly, aspects relate to surgical cuttinginstruments and systems capable of both high-speed cutting and, in someembodiments electrical probing or evoked potential monitoring functions,as well as procedures utilizing such a device.

Surgical cutting instruments are commonly used to perform a variety ofprocedures. For example, many neurotological surgical operations involvepartial or total removal of bone or other hard tissue via a high-speedrotating bur or other cutting tips. Exemplary procedures in this fieldinclude cochleostomies, removal of acoustic neuroma tumors, and removalof the scutum in a tympanoplasty. Numerous other surgical operationshave similar bone/hard tissue cutting or removal requirements. Thetypical surgical cutting instrument is akin to a drill, including adrill handpiece that rotates a cutting implement. The handpiece houses amotor and a chuck or other adapter, with the chuck being rotated by themotor under the control of a foot-operated or finger-operated switch.

Human nerves are often in close proximity to an area of bone or tissueremoval in many surgical procedures. Thus, one overarching concernrelating to these types of surgical cutting operations and instrumentsis the danger of severing or otherwise damaging nerves throughinadvertent cutting or excessive heat. For example, when a straight burcutting instrument is used for bulk bone removal, a surgeon might beconcerned with over-aggressive cutting as well as wobble and associatednerve damage. As another example, a curved bur cutting instrument usedin finer cutting applications might have a high thermal discharge at thecutting bur giving rise to nerve damage concerns.

Indeed, often times the above-described surgical cutting instrumentsrequire additional steps and instruments for measuring nerve location tocomplete a surgical procedure. For example, a mastoidectomy can entailexposing the mastoidperiostiem and then carefully drilling/removing themastoid bone using a cutting instrument and microscope. Moreover, apatient may have abnormal anatomy due to congenital or iatrogenicdefects that places nerves in unanticipated regions such that theanatomical landmarks a surgeon might otherwise normally refer to as aguide for neural tissue may not exist. While carrying out suchprocedures, a surgeon can be required to sequentially cut with asurgical cutting instrument and then probe a cut area for nerves with aseparate evoked potential monitoring system handpiece. This is clearlytime-consuming and thus undesirable.

SUMMARY

Embodiments of the present invention relate to a surgical cuttinginstrument for use with a motor assembly having a motor and a drivemechanism. The cutting instrument includes an elongate drive memberdefining a proximal section and a distal section, a cutting tip securedto the distal section of the drive member, and a non-conductive couplingbody adapted for connection to a motor assembly drive mechanism, thecoupling body secured to the proximal section of the drive member. Theinstrument also includes a housing maintaining the coupling body and theproximal section of the drive member, and an electrical connector forconnection to a stimulating energy source. In particular, the electricalconnector is in electrical communication with the cutting tip via anelectrical pathway established by at least the drive member. In oneembodiment, the cutting instrument has a curved configuration; inanother embodiment, the cutting instrument is straight.

Other embodiments of the present invention relate to a surgical cuttingsystem including a surgical cutting instrument, a motor assembly, and anevoked potential monitor system. The surgical cutting instrumentincludes an elongate drive member, a cutting tip, a non-conductivecoupling body, a housing, and an electrical connector in electricalcommunication with the cutting tip via an electrical pathway. The motorassembly includes a drive motor and a drive mechanism driven by themotor. The coupling body and the drive mechanism are configured toreleasably mount to one another. The coupling body electrically isolatesthe drive mechanism from the cutting tip electrical pathway uponmounting of the cutting instrument to the motor assembly. The evokedpotential monitor system includes an energy source selectivelyelectrically coupled to the cutting tip via the electrical connector forapplying a stimulating energy to the cutting tip via the electricalconnector and the electrical pathway.

Yet other embodiments of the present invention relate to a method ofperforming a surgical cutting procedure including providing a surgicalcutting instrument having an elongate drive member, a cutting tip, anon-conductive coupling body, a housing, and an electrical connectorelectrically connected to the cutting tip via an electrical pathway. Amotor assembly is coupled to the coupling body. An evoked potentialmonitoring system is connected to the cutting instrument via theelectrical connector such that an energy source of the evoked potentialmonitor system is in electrical communication with the cutting tip. Themotor assembly is operated to effectuate performance of a cuttingoperation with the cutting tip. A stimulation energy is applied to thecutting tip to facilitate detecting a proximity of the cutting tip to anerve by the evoked potential monitor system.

Yet other embodiments of the present invention relate to a surgicalcutting instrument for use with a motor assembly including a motorhousing and a motor driving a drive mechanism. The surgical cuttinginstrument includes an elongate drive member, a cutting tip, anon-conductive coupling body, and a non-conductive instrument housing.The cutting tip is secured to a distal section of the elongate drivemember, whereas the non-conductive coupling body is secured to aproximal section thereof. Further, the non-conductive coupling body isconfigured for selective attachment to the drive mechanism of the motorassembly. The instrument housing is provided apart from the housing, andmaintains a portion of the elongate drive member and the coupling body.Upon mounting to the motor assembly, the coupling body and theinstrument housing isolate the cutting tip from electrical ortriboelectric noise generated by the motor assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one embodiment surgical cuttinginstrument in accordance with principles of the present invention.

FIG. 2 is an exploded, cross-section view of the surgical cuttinginstrument of FIG. 1.

FIG. 3 is a cross-sectional view of another embodiment surgical cuttinginstrument in accordance with principles of the present invention.

FIG. 4 is a cross-sectional view, including portions shownschematically, of another embodiment surgical cutting instrument inaccordance with principles of the present invention in conjunction witha motor assembly.

FIG. 5A is a cross-sectional view of another embodiment surgical cuttinginstrument in accordance with principles of the present invention inconjunction with a motor assembly.

FIG. 5B is a cross-sectional view of a portion of the instrument of FIG.5A.

FIG. 6 is a schematic illustration of a surgical cutting system inaccordance with principles of the present invention.

FIG. 7 is a schematic illustration of another surgical cutting system inaccordance with principles of the present invention.

DETAILED DESCRIPTION

One embodiment of a surgical cutting instrument 20 is shown in FIGS. 1and 2. The surgical cutting instrument 20 includes an outer support tube22, an elongate drive member 24, a cutting tip 26, a coupling body(e.g., a tang) 28, a housing 30, and an electrical connector 32. Ingeneral terms, the elongate drive member 24 is coaxially disposed withinthe outer support tube 22. The cutting tip 26 is connected to andextends distally from the elongate drive member 24. The coupling body 28is secured to the elongate drive member 24. The housing 30 maintains theouter support tube 22 and the coupling body 28. The electrical connector32 delivers electrical energy from a source (not shown) to the cuttingtip 26 via an electrical pathway established, at least in part, by thedrive member 24, with the coupling body 28 electrically isolating theelectrical pathway from components (e.g., a motor assembly) otherwiseproximally mounted to the coupling body 28.

In some embodiments, a journal bearing is established between theelongate drive member 24 and the outer tube 22 upon rotation of theelongate drive member 24 relative to the outer tube 22 (e.g., via amotor assembly (not shown)). In some embodiments, the surgical cuttinginstrument 20 and components thereof provide one or more features thatfacilitate extremely high rotational speeds (on the order of 80,000RPM), with the outer tube 22, and thus the elongate drive member 24,defining one or more curved segments where desired. U.S. applicationSer. No. 10/776,835 (filed Feb. 11, 2004 and entitled “High SpeedSurgical Cutting Instrument”), the teachings of which are incorporatedherein by reference, describes examples of such features in accordancewith one embodiment.

The outer tube 22 is an elongate tubular body, defining a proximalregion 40 terminating at a proximal end 42, a distal region 44terminating at a distal end 46, and an intermediate region 47 betweenthe proximal and distal regions 40, 44. Further, the outer tube 22defines a lumen 48 (best shown in FIG. 2) extending from the proximalend 42 to the distal end 46. Thus, an inner surface 50 of the outer tube22 forms the lumen 48.

The outer tube 22 can assume a variety of longitudinal shapes. As shownat 52 in FIG. 1, in one embodiment, the outer tube 22 includes a curvedsegment at or along one or both of the intermediate region 47 and/or thedistal region 44. In addition, the outer tube 22 is constructed tofacilitate formation of a rotating journal bearing (i.e., frictionalsliding journal bearing) relative to the elongate drive member 24 in theembodiment shown in FIG. 1. As will be described in greater detailbelow, the outer tube 22 acts as a part of an electrical pathway in someembodiments of the present invention. As such, at least a portion of theouter tube 22 is constructed of an electrically conductive material suchthat the outer tube 22 is capable of being in electrical communicationwith the elongate drive member 24 and the electrical connector 32. Theouter tube 22 is also constructed of a material selected to provide theouter tube 22 with high strength, high stiffness characteristicssatisfying dimensional and curvature constraints as desired. In oneembodiment, the outer tube 22 is made of conventional surgicalinstrument materials, such as stainless steel.

Returning to FIG. 2, the elongate drive member 24 includes a proximalsection 60 and a distal section 62. The elongate drive member 24 has anoverall longitudinal length greater than the outer tube 22 such that,upon final assembly, the proximal and distal sections 60, 62 extend fromthe ends 42, 46, respectively, of the outer tube 22. The elongate drivemember 24 is also constructed to be relatively thin. In particular, thethinness of the elongate member 24, in combination with the absence of aball bearing assembly as part of the instrument 20, allows the lumen 48to have a relatively small diameter, such that even with a preferred,minimized outer diameter, the outer tube 22 can have sufficientthickness to provide requisite stiffness when an appropriate material(e.g., 17-4 stainless steel) is selected for the outer tube 22.

In one embodiment, the elongate drive member 24 is also constructed tofacilitate a rotating journal bearing relative to the outer tube 22while maintaining structural integrity along a curved axial length. Inparticular, the elongate drive member 24 is formed to exhibit highstrength and good fatigue characteristics. Additionally, at least aportion of the elongate drive member 24 is made of a conductive materialto facilitate electrical communication between the outer support tube22, the elongate drive member 24, and, as will be described in greaterdetail below, the cutting tip 26. Thus, in one embodiment, the elongatedrive member 24 is formed of M2 hardened tool steel. Alternatively,other materials exhibiting the desired durability, fracture resistance,electrical conductivity, etc., can be employed for the elongate drivemember 24.

Assembly of the surgical cutting instrument 20 is described in greaterdetail below. With respect to assembly of the outer tube 22 and theelongate drive member 24, however, a lubricant (not shown) is preferablyprovided along a length of the interface between the two components 22,24 to facilitate formation of a hydrodynamic journal bearingtherebetween. The elongate drive member 24 effectively “floats” relativeto the outer tube 22 upon rotation of the elongate drive member 24 as itis supported by a hydrodynamic effect. As described in greater detailbelow, intimate contact between the outer tube 22 and the drive member24 ensures that the desired electrical pathway is constantly maintainedbetween the components 22, 24, such that the lubricant need notnecessarily be electrically conductive. In another embodiment, thelubricant is electrically conductive and further facilitates electricalcommunication between the outer tube 22 and the elongate drive member24. Thus, in one embodiment the lubricant is an electrically conductivegrease lubricant, such as a lubricant available from Nye Lubricants ofFairhaven, Mass., under the trade name Nyogel 756G. However, in light ofthis description, it should be understood that other conductivelubricant materials can be employed.

The cutting tip 26 can assume a variety of forms, and in one embodimentincludes a cutting bur 70 and an attachment end 72. The attachment end72 is sized to receive the distal section 62 of the elongate drivemember 24. To this end, the cutting tip 26 can be secured to the distalsection 62 of the elongate drive member 24 via a number of knownprocesses such as, for example, welding, braising, press-fitting,thermal shrink fitting, adhesive, etc. Alternatively, the elongate drivemember 24 and the cutting tip 26 can be integrally formed such as bymachining the elongate drive member 24 and the cutting tip 26 from asingle piece of stock material. Regardless, the elongate drive member 24and the cutting tip 26 should be secured in a manner to facilitateelectrical communication between the two components 24, 26. As such, thecutting tip 26 is formed of electrically conductive material, such asnickel alloy materials in one embodiment. While the cutting tip 26 mightinclude such cutting structures as small diamond burs, it should beunderstood that the spaces between such structures and the tissue andfluid associated with cutting operations allow an electrical interfacebetween a cutting area (not shown) and conductive portions of thecutting tip 26. Regardless, the overall form of the cutting bur 70 canassume a variety of shapes and sizes known in the art (e.g., 2 mmfluted, 1 mm diamond, etc.). Alternatively, the cutting tip 26 canassume any other form appropriate for tissue and/or bone cuttingprocedures.

The coupling body 28 can assume a variety of forms but is generallyconfigured to facilitate connection of a motor assembly (not shown) tothe elongate drive member 24. As will be understood in greater detailbelow, some embodiments of the present invention require that the motorassembly be electrically insulated from the elongate drive member 24. Inone such embodiment, the coupling body 28 is formed of a non-conductivematerial in order to ensure that the motor assembly is electricallyinsulated from the elongate drive member 24. For example, in oneembodiment the coupling body 28 is formed of non-conductive ceramic orplastic material, such as an Ultem® resin available from GE Plastics ofPittsfield, Mass. or other polymeric or ceramic materials exhibitingsimilar tensile strength. Alternatively, the coupling body 28 can beformed from metal/metal alloy with a thin, non-conductive exteriorcoating.

It should be understood that the motor assembly (not shown) can be ofthe type typically employed with surgical cutting instruments, such aselectric, battery-powered, or pneumatic. One exemplary motor assembly isavailable from Medtronic-Xomed of Jacksonville, Fla. under the tradename Visao®. Alternatively, other types of motors or drill drive systemscan be employed. In general terms, the motor assembly includes a housingmaintaining a drive motor. The motor drives (e.g., rotates) a shaft orother drive mechanism that is connected to the elongate drive member 24upon mounting of the cutting instrument 20 to the motor assembly. Tothis end, the drive mechanism can include a connector of a typetypically employed with surgical cutting instruments that facilitatesconnection or coupling to the cutting device, such as a mechanicalconnector (e.g., the drive mechanism can include a chuck extending froma motor-driven shaft opposite the drive motor), non-contactingair-driven coupling, etc. With this in mind the coupling body 28 ofFIGS. 1 and 2 is adapted for use with a mechanical-type drive mechanismconnector (e.g., chuck) for selective mounting of the coupling body 28to the drive mechanism, with the coupling body 28 electrically isolatingthe drive mechanism, and thus the motor, from the elongate drive member24.

In more specific terms, and in one embodiment, the coupling body 28 isdefined by a distal portion 80 and a proximal portion 82. The distalportion 80 forms a first passage 84 extending from a distal end 86thereof. The first passage 84 defines a diameter sized to looselyreceive the proximal end 42 of the outer tube 22, serving to generallyalign the outer tube 22 relative to the proximal portion 82.Importantly, the distal portion 80 can rotate freely about the outertube 22. The proximal portion 82 forms a second passage 87 extendingproximally from the first passage 84. The second passage 87 is sized toreceive and maintain the proximal section 60 of the elongate drivemember 24. In this regard, the coupling body 28 can be further securedto the proximal section 60 of the elongate drive member 24 by a varietyof techniques. For example, the coupling body 28 can be over-molded ontothe elongate drive member 24. However, in one embodiment, the couplingbody 28 is further secured to the proximal section 60 of the elongatedrive member 24 by an epoxy, such as Loctite® M-31CL™ available fromHenkel Loctite Corp. Alternatively, other epoxies or adhesives can beused.

The proximal portion 82 of the coupling body 28 forms a groove 90 and atang 92 each adapted to facilitate coupling to the motor assembly drivemechanism (not shown), for example a chuck. The tang 92 serves as aguide surface that promotes rapid, consistent assembly of the drivemechanism to the coupling body 28. Once again, however, the couplingbody 28 can assume a variety of other configurations.

Similar to the coupling body 28, the housing 30 can assume a variety offorms and is generally configured to support the outer tube 22 as wellas facilitate attachment of the coupling body 28, and elongate drivemember 24, to a motor assembly or “handpiece” (not shown). Theinstrument housing 30 is provided apart from any housing associated withthe motor assembly/handpiece. In one embodiment, the housing 30 isformed from a non-conductive material such that the housing 30 alsofacilitates electrical isolation of the motor assembly from the elongatedrive member 24, and in particular from the cutting tip 26, uponassembly of the cutting instrument 20 to the motor assembly. Forexample, in one embodiment the housing 30 is formed of a liquid crystalpolymer. To this end, the housing 30 can be insert molded over the outertube 22. Alternatively, a variety of other assembly techniques, such asgluing, welding, press fitting, thermal shrink fitting, etc., areequally acceptable. The housing 30 can incorporate a variety of featuresthat facilitate mounting to the motor assembly. In one embodiment, thehousing 30 forms a central aperture 100 having an open proximal end 102defined by a plurality of spaced fingers 104. The central aperture 100is sized to receive at least a portion of the motor assembly (e.g., acollet otherwise maintaining a chuck portion of the motor assembly drivemechanism), with the fingers 104 serving to capture the motor assemblywithin the aperture 100. In addition, or alternatively, the housing 30can be configured to facilitate attachment to the motor assembly viasnap fit, threads, interference fit, etc. Further, with the embodimentsof FIGS. 1 and 2, the housing 30 defines a passage 106 fluidly connectedto the aperture 100. The passage 106 is sized to maintain the outer tube22 and can be formed during an insert molding procedure.

The electrical connector 32 includes an insulated wire 110 having anexposed end 112. For purposes of clarity, the size of the wire 110 isexaggerated in FIGS. 1 and 2. As shown in FIG. 1, the exposed end 112 issoldered to an outer surface of the outer support tube 22, with a distalportion of the wire being supported by the housing 30. However, inalternative embodiments, the electrical connector 32 can be welded,attached with a metal connector (e.g., screw), press fitted, crimped, orattached with conductive adhesive to the outer support tube 22 orintegrally formed therewith. In general terms, the electrical connector32, and in particular the wire 110, can be electrically connected to anypoint along a length of the outer tube 22; however, the area nearest thehousing 30 or encompassed within the housing 30 is most ergonomical.

The surgical cutting instrument 20 is assembled by coaxially disposingthe elongate drive member 24 within the lumen 48 of the outer tube 22.As previously described, in one embodiment a grease lubricant (notshown) is disposed along at least a portion of, preferably an entiretyof, an interface between the elongate drive member 24 and the innersurface 50 of the outer tube 22. The outer tube 22 is assembled to thehousing 30 as shown in FIG. 1, with the intermediate region 47 and thedistal region 44 extending distal to the housing 30. As mentioned, inone embodiment, the insulated wire 110 of the electrical connector 32 isin electrical communication with the outer tube 22 as it is soldered toa portion of the outer tube 22.

The housing 30 can be insert molded over both the outer tube 22 and aportion of the electrical connector 32 extending from the outer tube 22,with the elongate drive member 24 then being placed within the lumen 48.Additionally, in one embodiment, an exterior non-conductive coating orsleeve (not shown) is formed or provided over the outer tube 22 distalthe housing 30. For example, in one embodiment, a non-conductive sleeve(e.g., a shrink tube of polyester) is fitted about an exterior portionof the outer tube 22 otherwise extending distally from the housing 30 tothe distal end 46. As will be understood in greater detail below, thenon-conductive coating or sleeve promotes the ability of the cutting tip26 to act as an electrical probe, preventing shunting of current tosurrounding tissue, bone, or other structures when a stimulation energyis applied thereto (as might otherwise occur were the metal tube 22 leftexteriorly “exposed”). Additionally, in one embodiment, variouspreferred design features of the surgical cutting instrument 20, such asmaterial selection and the resultant journal bearing, allow for onlylimited exposure of the elongate drive member 24 distal to the distalend 46 of the outer tube 22, represented at B in FIG. 1. For example,the exposed length B of the elongate drive member 24 is preferably notgreater than 0.1 inch (2.54 mm), and more preferably not greater than0.05 inch (1.3 mm). In light of this disclosure, it should be understoodthat this limited exposure of the elongate drive member 24 (that isotherwise electrically conductive) to the environment can also promotemore effective use of the cutting tip 26 as an electrical probe byreducing potential electrical shunting.

Regardless, the coupling body 28 is secured to the proximal section 60of the elongate drive member 24, whereas the cutting tip 26 is attachedto the distal section 62 of the elongate drive member 24. With thisassembly, the insulated wire 110 of the electrical connector 32 is inelectrical communication with the outer support tube 22, which in turnis in electrical communication with the elongate drive member 24, whichin turn is in electrical communication with the cutting tip 26. Thisforms an electrical pathway consisting of the electrical connector 32,the outer support tube 22, the elongate drive member 24, and the cuttingtip 26.

As alluded to above, the instrument 20 provides an extremely stableelectrical pathway between the electrical connector 32 and the cuttingtip 26. In one embodiment, intimate contact between the outer tube 22and the elongate drive member 24 (due, at least in part, to the bend)establishes and consistently maintains the continuous electricalcoupling between the two components 22, 24, such that any lubricantprovided between the outer tube 22 and the drive member 24 need not beelectrically conductive. In alternative embodiments, the use of anelectrically conductive grease for the journal bearing acts to furthermaintain continuous electrical communication between the outer supporttube 22 and the elongate drive member 24. Regardless, the journalbearing acts to maintain continuous electrical communication between theelectrical connector 32 and the cutting tip 26 both at rest and duringhigh-speed cutting operations, for example those reaching greater than20,000 RPM, and in particular, those reaching approximately 80,000 RPM.In turn, the non-conductive coupling body 28 and non-conductive housing30 act to insulate the motor assembly (not shown) from the electricalpathway to prevent interruption or misdirection of electrical currenttraveling through the electrical pathway to the cutting tip 26. Thiselectrical isolation of the motor assembly is particularly importantwhen the motor assembly (or handpiece) is grounded. In particular, itprevents current from being shunted away from the electrical pathwaybetween the electrical connector 32 and the cutting tip 26.

In addition, by electrically isolating the patient-applied component(i.e., the cutting tip 26) from the motor assembly (not shown), thenon-conductive coupling body 28 and housing 30 serve to prevent theconduction of any electrical or triboelectric noise from the motorassembly to the cutting tip 26 that might otherwise cause interferencewith other devices positioned near or at the surgical site that relyupon biosignals from the patient for proper operation. Thus, the cuttinginstrument 20 is highly compatible for use with other devices thatamplify low-level biosigns such as EMG, EKG, EEG, ABR, etc., for thepurpose of intraoperatively monitoring patient status. In fact, inalternative embodiments, the electrical conductor 32 can be eliminated,with the resultant cutting instrument providing a distinct improvementover existing designs when used in conjunction with a separate patientmonitoring device.

While the surgical cutting instrument 20 has been described as providinga curved shaft configuration capable of high speed operation, in otherembodiments, a more conventional straight shaft design can be employedand are capable of supporting larger shaft diameters and cutting tipdiameters of 7 mm or greater (for example, for bulk bone removalprocedures). For example, the surgical cutting instrument 20 can beformed with the outer tube 22, and thus the elongate drive member 24,assuming a straight or linear shape. Alternatively, FIG. 3 illustratesanother embodiment surgical cutting instrument 120 in accordance withprinciples of the present invention that includes an elongate drivemember 124, a cutting tip 126, a coupling body 128, a housing 130, anelectrical connector 132, and a bearing assembly 134. The surgicalcutting instrument 120 can be used as a “nose piece,” similar to what issometimes termed a “bur extender,” that can be fitted on the front of amotor assembly or “handpiece” (not shown) to provide additionalstability (e.g., to prevent wobble) to the elongate drive member 124 andcutting tip 126. In addition, and as described below, the surgicalcutting instrument 120 is uniquely configured to establish an electricalpathway from the electrical connector 132 to the cutting tip 126.

In general terms of assembly and function, the elongate drive member 124is coaxially disposed within the housing 130. The cutting tip 126 isconnected to and extends distally from the elongate drive member 124.The coupling body 128 is secured to the elongate drive member 124 and isadapted for connection to a drive mechanism connector (not shown) of amotor assembly (not shown). The housing 130 is provided apart from themotor assembly, and maintains the electrical connector 132 and thebearing assembly 134. Thus, the housing 130 acts to maintain and supportthe elongate drive member 124 (as well as the cutting tip 126 securedthereto) and the bearing assembly 134. Finally, an electrical pathway isestablished from the electrical connector 132 to the cutting tip 126,for example via the bearing assembly 134 and the drive member 124.However, it should be noted that instead of the conductive couplingrelationship shown, the cutting instrument 120 can be configured toestablish an inductive or capacitive coupling to the cutting tip 126.

The elongate drive member 124 includes a proximal section 160 and adistal section 162. As shown, the elongate drive member 124 has anoverall longitudinal length greater than that of the housing 130 suchthat upon final assembly, the distal section 162 extends from thehousing 130. At least a portion of the elongate drive member 124 isformed of a conductive material in order to facilitate electricalcommunication with the cutting tip 126, as will be described in greaterdetail below. Some appropriate materials include stainless steel andtool steel materials, such as M-Series tool steels, A-Series toolsteels, etc. Alternatively, other materials exhibiting the desireddurability, fracture resistance, conductivity, etc., can be employed forthe elongate drive member 124.

The coupling body 128 can assume a variety of forms, but is generallyconfigured to facilitate connection of a motor assembly drive mechanismconnector (not shown) to the elongate drive member 124. As a point ofreference, the motor assembly (not shown) and the drive mechanismconnector can assume a variety of forms (e.g., can include a chuck), aspreviously described in association with other embodiments. In oneembodiment, the coupling body 128 is defined by a distal portion 180 anda proximal portion 182. The distal portion 180 of the coupling body 128is configured to facilitate coupling of the elongate drive member 124 tothe coupling body 128. The coupling body 128 can be secured to theproximal section 160 of the elongate drive member 124 by a variety oftechniques, such as via adhesives, male and/or female threads,overmolding the coupling body 128 over the elongate drive member 124,and others. The proximal portion 182, in turn, is configured to serve asa guide surface that promotes rapid, consistent assembly of the motorassembly drive mechanism connector (e.g., a chuck) to the coupling body128. Once again, however, the coupling body 128 can assume a variety ofother forms, as can assembly of the coupling body 128 to the elongatedrive member 124 and/or to the motor assembly drive mechanism.

Similar to other embodiments previously described, the coupling body 128is formed of a non-conductive material and serves to assist inelectrically isolating the elongate drive member 124 from the motorassembly (not shown). As such, the non-conductive coupling body 128 canbe formed of a variety of non-conductive materials as previouslydescribed.

The cutting tip 126 can also assume a variety of forms, including thosepreviously described. The cutting tip 126 includes a cutting bur 170 andan attachment end 172. The attachment end 172 is configured to receivethe distal section 162 of the elongate drive member 124. To this end,the cutting tip 126 can be secured to the distal section 162 of theelongate drive member 124 via a number of known methods such as, forexample, welding, braising, press-fitting, thermal shrink fitting,adhesive, male and/or female threads, etc. The elongate drive member 124and the cutting tip 126 can alternatively be integrally formed such asby machining the elongate drive member 124 and the cutting tip 126 froma single piece of stock material. Additionally, the cutting bur 170 canassume a variety of shapes and sizes known in the art (e.g., 2 mm, 1 mmdiamond, etc.). Regardless, the elongate drive member 124 and thecutting tip 126 are secured together such that they are in electricalcommunication, as previously described in association with otherembodiments.

The housing 130 can assume a variety of forms and is generallyconfigured to maintain the elongate drive member 124, the electricalconnector 132, and the bearing assembly 134, as well as facilitatemounting of the cutting instrument 120 to a motor assembly (not shown).To this end, the housing 130 can be insert molded over a portion of theelectrical connector 132 and the bearing assembly 134. Alternatively, avariety of other manufacturing techniques, such as gluing, welding,press-fitting, thermal shrink fitting, etc., are equally acceptable. Thehousing 130 can incorporate a variety of features that facilitateassembly to the motor assembly, including those previously described.For example, in one embodiment, the housing 130 forms a central aperture200 having an open proximal end 202 configured for attachment to acorresponding component (e.g., a collet) of the motor assembly viamethods known to those of ordinary skill in the art. The centralaperture 200 is sized to receive and capture at least a portion of themotor assembly. In addition, or alternatively, the housing 130 can beconfigured to facilitate attachment to the motor assembly via snap fits,threads, interference fit, etc. In one embodiment, the housing 130 isformed of a non-conductive material (e.g., a liquid crystal polymer) toassist in electrically isolating the motor assembly from an electricalpathway formed by the cutting instrument 120 as described below.

The electrical connector 132 is configured to facilitate delivery of astimulation energy from an energy source (not shown) to the cutting tip126 via the electrical pathway. As such, in one embodiment, theelectrical connector 132 includes insulated wire 210 having an exposedend 212. As will be described in greater detail below, the insulatedwire 210 can be connected to monitoring systems, such as the energysource of a nerve monitoring system (not shown). As shown in FIG. 3, theinsulated wire 210 has been overmolded into the housing 130, with theexposed end 212 in contact with the bearing assembly 134. In particular,the exposed end 212 is soldered or otherwise electrically coupled (e.g.,metal fastener, conductive adhesive, crimping, press-fit, etc.) to thebearing assembly 134. In other embodiments, the electrical connector 132can establish an electrical pathway to the cutting tip 126 via othermeans. For example, the insulated wire 210 can be connected to a wirebrush, such as a beryllium brush similar to those used in motorassemblies (not shown) that is in contact with the elongate drive member124.

In one embodiment, the bearing assembly 134 is a ball bearing-typedevice, and includes an inner race or ring 220, an outer race or ring222, and rolling elements (or ball bearings) 224, all of which areformed of electrically conductive material, such as stainless steel. Thebearing assembly 134 can also include a bearing retainer ring, whichneed not be formed of electrically conductive material in someembodiments. The bearing assembly 134, and in particular the inner ring220, defines a bore configured to coaxially receive the elongate drivemember 124. It should be noted that the elongate drive member 124 isreceived within the inner ring 220 with sufficient intimacy to create acontinuous electrical pathway between the two components 124, 220.

From the previous description, it will be understood that the bearingassembly 134 acts as an electrical pathway between the electricalconnector 132 and the elongate drive member 124, such that the two arein electrical communication. It has been surprisingly found thatpassivated bearings, and bearings lubricated with non-conductivelubricant, or not otherwise lubricated, can interfere with forming anelectrical pathway between the electrical connector 132 and the elongatedrive member 124. For example, the bearing assembly 134 is designed withsmall gaps between the rolling elements 224 and the races 220, 222 thatallow the rolling elements 224 to effectively float in instances of timeduring high-speed operation. Further, the rolling elements 224 may haveeccentricities that result in selective contact between the rollingelements 224, the outer ring 222, and the inner ring 220. As such, inone embodiment, the bearing assembly 134 includes conductive grease (notshown) to fill gaps (not shown) between the rolling elements 224 and theinner ring 220 and the outer ring 222. As such, in one embodiment thebearing assembly is lubricated with a conductive grease, such as Nyogel®756G available from Nye Lubricants of Fairhaven, Mass. As mentionedpassivation layers on the rolling elements 224, such as chromium oxideand/or nickel oxide, are often used to increase corrosion resistance andhardness of the rolling elements, but can serve to render themelectrically non-conductive. As such, in one embodiment the rollingelements 224 are formed of non-passivated, stainless steel. Importantly,it has been found that by incorporating such features, the bearingassembly 134 is capable of forming a continuous electrical pathway, orcontinuous electrical communication, with the elongate drive member 124and the electrical connector 132 while the cutting tip 126 is at restand while it is turning at relatively high rotational speeds greaterthan 20,000 RPM, and in one embodiment at speeds approaching 80,000 RPM.

Upon final assembly, a stable electrical pathway is established from theelectrical connector 132 to the cutting tip 126. Conversely, thecoupling body 128, as well as the housing 130, acts to electricallyinsulate motor assembly (not shown) from the electrical pathwaydescribed upon mounting of the cutting instrument 120 to the motorassembly. In sum, in one embodiment, the bearing assembly 134 includesmaterials and is configured such that the electrical pathway iscontinuously maintained during operation, without intermittentinterruption, during high-speed rotation of the elongate drive member124, such as at speeds greater than 20,000 RPM, and as high as 80,000RPM. The non-conductive coupling body 128 electrically isolates thedrive member 124 (that is otherwise part of the electrical pathway) fromthe corresponding component of the motor assembly drive mechanism towhich the coupling body 128 is attached, whereas the non-conductivehousing 130 (that otherwise is in contact with the electrical pathway)electrically isolates the cutting instruments 120 from correspondingcomponent(s) of the motor assembly (e.g., motor assembly housing orcollet) to which the instrument housing 130 is attached. Depending upona desired distal extension of the elongate drive member 124 from thehousing 130, the elongate drive member 124 can further include anon-conductive, exterior coating or sleeve to prevent shunting ofelectrical current away from the desired electrical pathway from theelectrical connector 132 to the cutting tip 126 and/or inadvertentcontact with the motor assembly.

In addition to ensuring a stable electrical pathway, the non-conductivecoupling body 128 and housing 130 serve to isolate the cutting tip 126from electrical or triboelectrical noise generated by a motor assembly(not shown) otherwise mounted to and rotating/driving the elongate drivemember 124. Thus, similar to the surgical cutting element 20 (FIG. 1)previously described, in alternative embodiments, the surgical cuttinginstrument 120 need not include the electrical connector 132, with theresultant instrument preventing the transmission of electrical ortriboelectrical noise to the cutting tip 126 in a manner that mightotherwise interfere with proper operation of a separate intraoperativepatient monitoring device.

A portion of another embodiment surgical cutting instrument 230 inaccordance with principles of the present invention in conjunction witha portion of a motor assembly 232 is shown in FIG. 4. The instrument 230includes an elongate drive member 234, a cutting tip 236, a couplingbody 238, a housing 240, a fluid coupling assembly 242 (referencedgenerally), and an electrical connector 244. For ease of illustration,the drive member 234, the cutting tip 236, the coupling body 238 andportions of the motor assembly 232 are shown schematically in FIG. 4. Asdescribed below, the instrument 230 operates in a manner similar toprevious embodiments, whereby the coupling body 238 is coupled to themotor assembly 232 (such as via a chuck 246) for rotating the cuttingtip 236. Further, a stimulating current delivered by the electricalconnector 244 flows to the cutting tip 236 via the fluid couplingassembly 242 as part of an evoked potential monitoring operation.

The drive member 234 is formed of a rigid, electrically conductivematerial (e.g., steel), and defines a distal portion 248, anintermediate portion 250, and a proximal portion 252. The distal portion248 is attached to or otherwise terminates at the cutting tip 236 andthus defines an axial length or extension of the cutting tip 236relative to the housing 240, and can assume a variety of lengths. Theproximal portion 252 terminates, or in one embodiment (as shown) forms,the coupling body 238. Regardless, in one embodiment, the intermediateportion 250 has an increased outer diameter as compared to the distaland proximal portions 248, 252 (at least in those regions immediatelyadjacent the intermediate portion 250), and is characterized as beingexteriorly exposed as compared to the distal and proximal portions 248,252. More particularly, in one embodiment an exterior of the drivemember 234 is encompassed by an electrically non-conductive, insulatingcoating 254 (referenced generally) in all regions except theintermediate portion 250. As a point of reference, a thickness of theinsulating coating 254 is exaggerated in FIG. 4 for clarity purposes.With embodiments in which the drive member 234 forms the coupling body238, the coupling body 238 is also covered by the coating 254 (it beingunderstood that for alternative embodiments in which the coupling body238 is formed apart from, and subsequently attached to, the drive member234, the coupling body 238 is either comprised of an electricallynon-conductive material and/or is coated with an electrically insulativecovering). Conversely, with embodiments in which the drive member 234forms the cutting tip 236, the cutting tip 236 is free of the insulativecoating 254. Regardless, the insulative coating 254 can take a varietyof forms and can be applied in a multitude of manners. For example, theinsulative coating 254 can be plastic shrink tubing, over moldedplastic, etc., formed of an electrically non-conductive material.

The cutting tip 236 and the coupling body 238 can assume any of theforms previously described. Thus, the cutting tip 236 can be a bur,cutting teeth, etc. As alluded to above, the coupling body 238 can beintegrally formed by the drive member 234 or provided separately. In oneembodiment, however, the coupling body 238 forms a groove 256 forreleasably engaging the chuck 246. Alternatively, the coupling body 238can assume other configurations commensurate with a correspondingcomponent of the motor assembly 232.

The housing 240 can incorporate various features previously describedand is formed from, or exteriorly coated with, an electricallynon-conductive material (e.g. the housing 240 can be formed ofelectrically insulative plastic). The housing 240 defines a distalregion 258, a proximal region 260, and a central passage 262. Thepassage 262 along the proximal region 260 is sized to matingly receive acorresponding housing 263 (illustrated schematically) of the motorassembly 232. Conversely, the distal region 258 forms the passage 262 tobe slightly greater than a diameter of the drive member 234 and isconfigured to maintain portions of the fluid coupling assembly 242 asdescribed below.

In one embodiment, the fluid coupling assembly 242 includes a conductivespacer 264 and tubing 266 fluidly connected to a source (not shown) ofelectrically conductive fluid. The conductive spacer 264 is formed of ahardened, electrically conductive metal and is mounted to the distalregion 258 of the housing 240 about the passage 262. In one embodiment,the conductive spacer 264 is a ring or other cylindrical shape definingan internal aperture 268 (referenced generally). The internal aperture268 has a diameter approximating an outer diameter of the intermediateportion 250 of the drive member 234 such that upon final assembly, theintermediate portion 250 is in approximate contact with the conductivespacer 264. In one embodiment, the conductive spacer 264 is porousand/or forms a radial opening(s) (one of which is illustrated at 270 inFIG. 4) for reasons described below.

The tubing 266 is formed of an electrically insulative material and isfluidly coupled at a proximal end (not shown) thereof to a source ofelectrically conductive fluid (not shown). For example, the electricallyconductive fluid can be saline, etc. Regardless, a distal end of thetubing 266 is fluidly connected to the conductive spacer 264, such asvia a port 272 formed in the housing 240. With this configuration,conductive fluid from the tubing 266 flows to the conductive spacer 264and then to an interior surface thereof, due to either a porosity orother formed opening 270 in the conductive spacer 264 as previouslydescribed.

Finally, the electrical connector 244 is an insulated wire or other bodycapable of delivering an electrical current. The electrical connector244 is electrically connected (e.g., welded) to the conductive spacer264. Thus, a portion of the electrical connector 244 can extend throughthe housing 240 as shown.

During use, the cutting instrument 230 is mounted to the motor assembly232 as shown. As a point of reference, the motor assembly 232 includesthe chuck 246 forming an internal flange 274 nestable within the groove256 of the coupling body 238 to facilitate engagement between thecoupling body 238/chuck 246. Further, the motor assembly 232 can includebearings 276 (drawn schematically) for supporting the drive member 234when rotated by driven rotation of the chuck 246/coupling body 238.Regardless, a stimulating current is delivered to the cutting tip 236 aspart of an evoked potential monitoring operation (that may or may notoccur in conjunction with cutting) by supplying a conductive fluid tothe conductive spacer 264 via the tubing 266. Due to a porosity and/orother opening 270 in the conductive spacer 264, the conductive fluidflows to an interface or spacing between the conductive spacer 264 andthe intermediate portion 250 of the drive member 234. As shown, aconductive fluid film 278 is formed, electrically coupling theconductive spacer 264 and the drive member 234. Where desired, seals(not shown) can be provided distal and/or proximal the conductive spacer264 to contain the conductive fluid at the conductive spacer 264/drivemember 234 interface. Regardless, an electrical pathway is establishedin which a stimulating current flows from electrical conductor 244(otherwise electrically connected to a stimulating energy source (notshown)), through the conductive spacer 264 and the conductive fluid film278, through the drive member 234, and to the cutting tip 236. Theinsulative coating 254 promotes use of the cutting tip 236 as anelectrical probe, preventing shunting of current to surrounding tissue.Further, the insulative coating 254 over the coupling body 238 (orother, non-conductive configuration of the coupling body 238) inconjunction with the non-conductive housing 240 electrically isolatesthe conductive pathway described above from the motor assembly 232 aswell as from a user otherwise handling the housing 240.

A portion of another embodiment surgical cutting instrument 280 inaccordance with the principles of the present invention in conjunctionwith a portion of the motor assembly 232 described above, is shown inFIG. 5A. The instrument 280 is similar in many respects to theinstrument 230 (FIG. 4) previously described, with like elements havinglike reference numbers. With this in mind, the instrument 280 includesthe elongate drive member 234, the cutting tip 236, the coupling body238, a housing 282, an electrical coupling assembly 284 (referencedgenerally), and the electrical connector 244. As described below, theinstrument 280 operates in a manner similar to previous embodiments,whereby the motor assembly 232 is coupled to the coupling body 238 (suchas via the chuck 246) for rotating the cutting tip 236. Further, astimulating current delivered by the electrical connector 244 (such asfrom a stimulating energy source (not shown)) flows to the cutting tip236 via the electrical coupling assembly 284 as part of an evokedpotential monitoring operation.

Similar to previous embodiments, the drive member 234 is formed of orcoated with a rigid, electrically conductive material, and defines thedistal portion 248, the intermediate portion 250, and the proximalportion 252. In this regard, the distal and proximal portions 248, 252are encompassed or covered by the electrically non-conductive,insulating coating 254 (referenced generally) as previously described,whereas the intermediate portion 250 is exteriorly exposed.

The housing 282 is, similar to previous embodiments, formed of anelectrically non-conductive material, such as plastic. In addition, thehousing 282 is configured to receive and maintain the electricalcoupling assembly 284, such as via a press fit. Alternatively, thehousing 282 can include additional internal features that more securelyreceive and maintain the electrical coupling assembly 284.

With additional reference to FIG. 5B, the electrical coupling assembly284 has a rotatable, bearing-type configuration, and includes an innerharness 286, an outer race 288, and a bearing body 290. The innerharness 286 is a generally ring-shaped body defining a base 292 and aplurality of fingers 294. The fingers 294 extend from the base 292 in agenerally longitudinal fashion (relative to the longitudinal axisdefined by the drive member 234), and combine to define an innerdiameter approximating an outer diameter of the intermediate portion 250of the drive member 234. Thus, upon final assembly, the fingers 294contact and engage the intermediate portion 250 of the drive member 234.To ensure consistent, continuous contact, in one embodiment, the fingers294 are “pre-loaded” to extend radially inwardly relative to the base292, combining to naturally assume an inner diameter less than an outerdiameter of the intermediate portion 250. Regardless, the inner harness286 is formed of an electrically conductive metal, such as steel. Theouter race 288 is similarly formed of a conductive metal, and is sizedfor securement to the housing 282 (e.g., press fit). Finally, thebearing body 290 is also electrically conductive, and is adapted tofacilitate rotation of the inner harness 286 relative to the outer race288. In one embodiment, the bearing body 290 is a ferro-fluid bearing.In addition, or as an alternative, the bearing body 290 can include oneor more ball bearing(s) formed of an electrically conductive material(e.g., steel). Regardless, the electrical connector 244 includes aninsulated wire electrically coupled (e.g., welded) to the outer race288, and thus, can extend through a thickness of the housing 282. Withthis configuration, an electrical pathway is established from theelectrical connector 244 to the cutting tip 236 via the electricalcoupling assembly 284 and the drive member 234.

Returning to FIG. 5A, during use the instrument 280 is connected to themotor assembly 232. For example, the chuck 246 (shown schematically) isconnected to the coupling body 238, with the bearings 274 (shownschematically) supporting the drive member 234 as previously described.Rotation of the chuck 246 causes the cutting tip 236 to rotate as partof a cutting operation. In addition, the instrument 280 can be employedto perform an evoked potential monitoring operation apart from and/orsimultaneously with tissue cutting. A stimulating current is deliveredvia the electrical connector 244 to the electrical coupling assembly284. In particular, the stimulating current is delivered to the outerrace 288 which, in turn conducts the current to the inner harness viathe bearing assembly 290. Intimate contact between the inner harness 286and the drive member 234 (regardless of whether the drive member 234 isrotating) conducts the applied current to the cutting tip 236. Onceagain, the insulative coating 254 prevents shunting of the currentdistal the housing 282, such that the current is focused upon thecutting tip 236. In addition, the insulative coating 254 (and/or othernon-conductive features associated with the coupling body 238) and thehousing 282 combine to insulate the motor assembly 232 from the current,as well as from a user otherwise handling the housing 282. In oneembodiment, the housing 282/electrical coupling assembly 284 serves as are-usable device, and thus can be repeatedly employed with a variety ofother drive members 234 (and thus, cutting tip 236 and coupling body238) configurations.

Regardless of an exact form of the surgical cutting instrument, asurgical cutting system can be provided in accordance with principles ofthe present invention. For example, FIG. 6 illustrates schematically asurgical cutting system 300 in accordance with one embodiment of thepresent invention. The surgical cutting system 300 includes a surgicalcutting instrument 310, a motor assembly 320, and an evoked potentialmonitor (or monitoring) system 330. It has been discovered that thesequential and separate process of probing then cutting, or vice-versa,as has been required in the past, is an area of potential improvementaddressed by the surgical cutting system 300, resulting, for example, inan early warning system for surgeons, alerting them to potentialiatrogenic injury to neural tissue. The simultaneous cutting and probingprocedure described below is safer for the patient (as compared to theconventional technique of alternating cutting and probing) as thesurgeon is no longer required to manually estimate the appropriate depthof cut between probing operations, and overall procedure time isreduced.

In one embodiment, the surgical cutting instrument 310 can be of asimilar design to the surgical cutting instruments 20 (FIG. 1), 120(FIG. 3), 230 (FIG. 4), or 280 (FIG. 5A), previously described, andgenerally includes a cutting tip 312 and an electrical connector 314,with the electrical connector 314 being electrically connected to thecutting tip 312 via an electrical pathway established by the cuttinginstrument 310 as previously described. The motor assembly 320 canassume any known form, and though shown schematically, generallyincludes a housing, a motor and a drive mechanism/connector, with thesurgical cutting instrument 310 and the motor assembly 320 adapted formounting to one another as previously described. Regardless, the motorassembly 320 and the surgical cutting instrument 310 are assembled suchthat motor assembly 320 drives (e.g., rotates) the cutting tip 312 inorder to perform a cutting operation. Notably, as described above, themotor assembly 320 is electrically isolated from the cutting tip 312 andthe electrical pathway upon mounting of the cutting instrument 310 tothe motor assembly 320.

The evoked potential monitor system 330 is a nerve integrity monitoringsystem, such as a NIM-Response® 2.0 nerve integrity monitoring systemavailable from Medtronic-Xomed, Inc. of Jacksonville, Fla. In generalterms, the evoked potential monitor system 330 is adapted to indicatewhen an energized probe, for example the cutting tip 312, is proximate anerve 340 (shown schematically) during a surgical cutting procedure. Forexample, the evoked potential monitor system 330 can include a patientinterface console maintaining circuitry and related equipment, theconsole being capable of providing a stimulating energy or current to aprobe via a stimulating energy source provided as part of the system330. In addition, electrodes (not shown) are placed on or in musclesthat are enervated by nerves in proximity to the expected cutting area,and are electrically coupled to the interface console. In this manner,the electrodes signal a response to the patient interface console'sinternal equipment (e.g., processor) when a stimulating currentenervates a nerve of concern. The evoked potential monitor system 330can also include alarms or other indicators as known in the art.Regardless, the electrical connector 314 is in electrical communicationwith both the evoked potential monitor system 330 and the cutting tip312 (via the electrical pathway). In this manner, the cutting tip 312serves as an electrical probe in conjunction with the evoked potentialmonitor system 330 when energized via the electrical connector 314.

During use, the evoked potential monitor system 330 prompts delivery(preferably continuous delivery) of a stimulating energy (e.g., current)through the electrical connector 314 to the cutting tip 312 via theelectrical pathway established by the cutting instrument 310. Thepreviously described surgical cutting instruments 20 (FIG. 1), 120 (FIG.3), 230 (FIG. 4), 280 (FIG. 5A) are several examples of instrumentscapable of ensuring that the stimulating energy is continuouslydelivered to the cutting tip 312. Properly placed patient electrodes(not shown) provide the evoked potential monitor system 330 withinformation indicative of a proximity of the cutting tip 312 to thenerve 340 in response to the applied stimulating current. For example,based on a comparison of the applied stimulating current with thesignaled information from the patient electrodes, the evoked potentialmonitor system 330 can detect, and/or provide the user with informationindicative of, the energized cutting tip 312 being at or within adistance D of the nerve(s) 340 of concern. The motor assembly 320,otherwise electrically isolated from the delivered stimulation energy,is simultaneously powered to rotate the cutting tip 312. Thus,simultaneous or substantially concurrent bone or tissue cutting andnerve probing functions can be performed by the system 300. Further,evoked potential monitoring can be performed via the cutting instrument310 with the motor assembly 320 deactivated (i.e., “off” or nototherwise driving the cutting instrument 310).

In a related embodiment surgical cutting system 350 shown in FIG. 7, asurgical cutting instrument 352 having a cutting tip 353 is againpowered by a motor assembly (illustrated schematically in FIG. 7 as partof the cutting instrument 352). The surgical cutting instrument 352 canassume any of the forms previously described. The cuttinginstrument/motor assembly 352 is electronically coupled to a surgicaldrill console 354, such as an XPS® console (Medtronic-Xomed, Inc., ofJacksonville, Fla.), having internal circuitry for controlling powerdelivered to the motor assembly 352. The system 350 further includes apatient monitor system 356 such as an evoked potential monitor system aspreviously described or a surgical navigation platform such as an imageguidance system available under the trade name LandmarX® Element IGSSystem from Medtronic-Xomed, Inc., of Jacksonville, Fla. Regardless ofan exact configuration, a communication link 358 (wired or wirelessconnection) is established between the surgical drill console 354 andthe patient monitoring system 356, with the patient monitor system 356being adapted (e.g., processor operating pursuant to appropriateprogramming) to prompt the surgical drill console 354 to disable themotor assembly 352 via a signal delivered through the communication link358.

More particularly, the patient monitoring system 356 is adapted tomonitor a patient 360 during a surgical procedure involving the surgicalcutting instrument 352. Patient monitoring can include evoked potentialmonitoring as previously described (e.g., a wire 362 can provide astimulating current from the patient monitor system 356 to the cuttinginstrument 352), or can be any other appropriate type of monitoring(e.g., image guidance). For example, in one embodiment, the patientmonitor system 356 includes EMG electrodes 364, 366 (“CH 1” and “CH 2”),along with a stimulation return path electrode 368 (“STIM RETURN”) and areference electrode 370 (“REFERENCE”). The EMG electrodes 364, 366 areplaced in muscles innervated by the nerves of concern. The return pathelectrode 368 provides a return path for the stimulation currentdelivered by the cutting tip 353 for embodiments in which the deliveredsimulation current is an isolated output that is not Earth referenced(and therefore requires its own isolated return). The referenceelectrode 370 provides a common reference between the patient 360 andthe patient monitor system 356 (required to center the EMG signal withinthe input range of the recording amplifiers). The return path andreference electrodes 368, 370 can be placed at a variety of locations onthe patient 360, such as the sternum, shoulder, forehead, etc.Regardless, upon detecting or otherwise determining that the cutting tip353 is proximate critical anatomy (e.g., nerve) of the patient 360, thepatient monitor system 356 is adapted to deliver a disabling signal tothe surgical drill console 354, prompting powering off of the cuttinginstrument/motor assembly 352. Thus, the system 350 effectively providesan automatic “kill-switch” to further ensure patient safety.

In light of the above, the advantages of non-sequential, high-speedcutting and probing or other monitoring can be realized in accordancewith embodiments of the present invention. The surgical cuttinginstrument and related surgical cutting system can be employed toperform virtually any surgical procedure requiring cutting of tissue andnerve monitoring, and especially with those procedures in which a smalldiameter, bur-type cutting tip is rotated at elevated speeds (e.g.,greater than 20,000 RPM) to effectuate desired tissue removal in anotherwise confined surgical access site. For example, the instrument andsystem of embodiments of the present invention can be employed toperform procedures such as mastoidectomy, discectomy, etc., to name buta few. Aspects of the present invention are not limited to anyparticular procedure, cutting tip style, or cutting speed. Regardless ofthe exact procedure, the instrument and system of embodiments of thepresent invention operate to provide both tissue cutting and evokedpotential (i.e., nerve) monitoring without the need for a separateelectrical probe instrument.

In alternative embodiments, the surgical cutting system includes one ormore other biosignal-based patient monitoring devices (e.g., EMG, EKG,EEG, ABP, etc.) in addition to the surgical cutting instrument and themotor assembly. With these embodiments, the cutting system may or maynot include an evoked potential monitor system, and the surgical cuttinginstrument may or may not include an electrical connector otherwiseelectrically connecting the cutting tip to an energy source. Regardless,non-conductive coupling body and housing components of the surgicalcutting instrument can take any of the forms described to electricallyisolate the motor assembly from the cutting tip. During use, thesurgical cutting instrument is mounted to the motor assembly, and themotor assembly is operated to drive (e.g., rotate) the cutting tip at asurgical site. Concurrent with operation of the motor assembly, thepatient monitoring device operates to monitor a condition of thepatient. To this end, electrical or triboelectric noise generated by themotor assembly is not conducted to the cutting tip (and thus notconducted to the surgical site) due to the non-conductive coupling bodyand housing, and thus does not interfere with operation of the patientmonitoring device(s).

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

1. A surgical cuffing instrument, for use with a motor assembly having amotor and a drive mechanism, the instrument comprising: an elongatedrive member defining a proximal section and a distal section; a cuffingtip secured to the distal section of the drive member; a non-conductivecoupling body adapted for releasable connection to a motor assemblydrive mechanism, the coupling body secured to the proximal section ofthe drive member, wherein the coupling body defines a distal portion anda proximal portion, the distal portion defining a first outer diameterand forming a longitudinal passage extending from a distal end withinwhich the proximal section of the elongate drive member is permanentlyaffixed, and the proximal portion forming a tang defining a second outerdiameter less than the first outer diameter; a housing maintaining thecoupling body and the proximal section of the drive member such that thecoupling body and the drive member are rotatable in tandem relative tothe housing; and an electrical connector in electrical communicationwith the cuffing tip via an electrical pathway established by at leastthe drive member, the electrical connector adapted for electricalconnection to an energy source.
 2. The cuffing instrument of claim 1,wherein the non-conductive coupling body is formed of polymericmaterial.
 3. The cuffing instrument of claim 1, wherein the housingmaintains a portion of the electrical connector.
 4. The cuffinginstrument of claim 1, wherein the housing is formed of non-conductivematerial.
 5. The cuffing instrument of claim 1, wherein the cuttinginstrument is configured such that energy flowing through the electricalconnector is continuously delivered to the cuffing tip during rotationof the drive member at a rotational rate of at least 20,000 RPM.
 6. Thecuffing instrument of claim 1, wherein the housing maintains a bearingassembly disposed between the housing and the elongate drive member, andfurther wherein the electrical connector is coupled to the bearingassembly such that the electrical pathway from the electrical connectorto the tip includes the elongate drive member and the bearing assembly.7. The cuffing instrument of claim 6, wherein the bearing assemblyincludes an inner race, an outer race, ball bearings, and a conductivegrease.
 8. The cuffing instrument of claim 1, wherein the longitudinalpassage includes a distal segment having a first diameter and anintermediate segment extending from the distal segment an defining asecond diameter less than the first diameter further comprising: anouter tube maintained by the housing, the outer tube defining a proximalregion terminating at a proximal end, a distal region terminating at adistal end, and a lumen extending from the proximal end to the distalend; wherein the elongate drive member is disposed within the lumen ofthe outer tube and the electrical pathway includes an interface betweenan inner surface of the outer tube and the elongate drive member; andfurther wherein the outer tube extends within the distal segment of thelongitudinal passage and the elongate drive member extends proximallybeyond the outer tube and into the intermediate segment of thelongitudinal passage.
 9. The cutting instrument of claim 8, wherein theinterface is at least partially defined by a journal bearing between theouter tube and the drive member, the electrical pathway including thejournal bearing.
 10. The cuffing instrument of claim 8, wherein an outersurface of the outer tube distal the housing is at least partiallycovered by a non-conductive material.
 11. The cutting instrument ofclaim 8, wherein the outer tube defines a curved segment distal thehousing.
 12. The cutting instrument of claim 8, wherein the cutting tipis a bur.
 13. The cutting instrument of claim 1, wherein the drivemember is straight.
 14. The cutting instrument of claim 1, wherein theelectrical connector contacts the drive member distal the non-conductivecoupling body.
 15. A surgical cutting system comprising: a surgicalcutting instrument, the cutting instrument including: an elongate drivemember, a cutting tip attached to a distal section of the drive member,a non-conductive coupling body attached to a proximal section of thedrive member, wherein the coupling body defines a distal portion and aproximal portion, the distal portion forming a longitudinal passageextending from a distal end and within which the drive member isreceived, and the proximal portion terminating at a proximal end of thecoupling body, a non-conductive housing maintaining the coupling bodyand the proximal section of the drive member, an electrical connector inelectrical communication with the cutting tip via an electrical pathwayestablished by at least the drive member; a motor assembly including amotor and a drive mechanism having a chuck configured for releasablemounting to the non-conductive coupling body such that in an un-mountedstate, the proximal end of the coupling body is free of the chuck and ina mounted state the proximal end is within the chuck and the drivemechanism is electrically insulated from the electrical pathway, whereinupon final assembly with the surgical cutting instrument, the motorrotates the coupling body and the drive member; and an evoked potentialmonitor system having an energy source selectively coupled to theelectrical connector for applying a stimulating energy to the cuffingtip via the electrical connector and the electrical pathway.
 16. Thesurgical cuffing system of claim 15, wherein the system is adapted suchthat as the motor rotates the cutting tip at speeds of at least 20,000RPM, the stimulating energy is continuously delivered from the energysource to the cutting tip.
 17. The surgical cutting system of claim 15,wherein the evoked potential monitor system is adapted to indicate whenthe cutting tip is proximate a nerve during a surgical cuttingprocedure.
 18. The surgical cuffing system of claim 15, wherein thecuffing tip is a bur.
 19. The surgical cuffing system of claim 15,wherein the cutting instrument housing is electrically non-conductiveand is provided apart from a housing of the motor assembly such thatupon mounting of the cutting instrument to the motor assembly, thecuffing instrument housing electrically isolates the electrical pathwayfrom portions of the motor housing otherwise in contact with the cuttinginstrument housing.
 20. A method of performing a surgical cuttingprocedure comprising: providing a surgical cutting instrument including:an elongate drive member, a cutting tip attached to a distal section ofthe drive member, a non-conductive coupling body fixedly attached to aproximal section of the drive member, a housing maintaining the couplingbody and the proximal section of the drive member, an electricalconnector in electrical communication with the cutting tip via anelectrical pathway established by at least the drive member;electrically connecting an evoked potential monitoring system to thecutting instrument via the electrical connector such that an energysource of the evoked potential monitor system is in electricalcommunication with the cutting tip; mounting the surgical cuttinginstrument to a motor assembly having a drive mechanism forming a chuckand a motor assembly housing provided apart from the surgical cuffinginstrument housing, wherein the non-conductive coupling body isreleasably received within the chuck and the surgical cutting instrumentelectrically isolates the motor assembly from the evoked potentialmonitoring system; delivering the cutting tip to a surgical site;operating the motor assembly to perform a cutting operation with thecuffing tip; applying a stimulation energy to the cutting tip via theenergy source; detecting a proximity of the cutting tip to a nerve basedupon reference to the stimulation energy; and releasing the surgicalcutting instrument from the motor assembly, including removing thenon-conductive coupling body from the chuck.
 21. The method of claim 20,wherein performing a cuffing operation with the cuffing tip includesrotating the cuffing tip at a speed of at least 20,000 RPM.
 22. Themethod of claim 20, wherein performing a cuffing operation and applyinga stimulation energy occur substantially simultaneously.
 23. The methodof claim 20, wherein the method is characterized by the motor assemblycontinuing to operate while a proximity of the cutting tip to a nerve isdetected.
 24. The method of claim 20, further comprising: automaticallydisabling power delivery to the motor assembly based upon the detectedproximity.
 25. A surgical cuffing instrument for use with a motorassembly including a motor housing and a motor driving a drivemechanism, the cuffing instrument comprising: an elongate drive memberdefining a proximal section and a distal section; a cuffing tip securedto the distal section of the drive member; a non-conductive couplingbody permanently affixed to the proximal section of the drive member andadapted for releasable attachment to the motor assembly drive mechanism,wherein the coupling body defines a distal portion and a proximalportion, the distal portion forming a longitudinal passage extendingfrom a distal end, and the proximal portion forming a groove along anexterior surface thereof; and a non-conductive housing provided apartfrom the motor assembly housing, the non-conductive housing encompassingthe coupling body and the proximal section of the drive member; whereinthe coupling body and the housing are configured to electrically isolatethe cutting tip from the motor assembly upon mounting of the cuttinginstrument to the motor assembly.